Motor accelerates and desacelerates by itself

[pabs]

Hi. I have a 2008 115hp Mercury Optimax, which starts easy and runs nice (up to 4000 and 5200 rpms). But after almost one hour running it, it begins to jump and looses power (never turns off). It also begins to acelerate and disacelerate by itself. None of the alarms sounds. It just does that.
Any idea what may be wrong?

 

[d.hauser]

Sound like it might be fuel line related. Check to see if the tank is venting properly. Also try pumping the bulb you may have a pin hole leak.

 

[Docksidemarineservices]

Sounds like it might be fuel lift pump related.

 

[pabs]

Sound like it might be fuel line related. Check to see if the tank is venting properly. Also try pumping the bulb you may have a pin hole leak.

Thanks for the prompt reply d.hauser...how do I check if the tank is venting properly_

 

[pabs]

Thanks Chris. I replaced the pump not too long ago. However, I did notice that when I pump it, it doesn´t get firm or hard. Could it be that the pump is damaged, or does not fit the line, or that there is a hole not visible? Several friends have told me that it might be the pump....

 

[Docksidemarineservices]

Thanks Chris. I replaced the pump not too long ago. However, I did notice that when I pump it, it doesn´t get firm or hard. Could it be that the pump is damaged, or does not fit the line, or that there is a hole not visible? Several friends have told me that it might be the pump....

Or it could be the mechanical fuel pump needs a rebuild.